1. Field of the Invention
The present invention relates to an ear type apparatus for measuring a bio signal and a measuring method therefor. More particularly, the present invention relates to an ear type apparatus for measuring a bio signal, such as temperature, respiration, pulse, and oxygen saturation, which can minimize a motion artifact caused by a subject's motion, and a measuring method therefor.
2. Description of the Related Art
When a human body is in an abnormal state, various changes may occur such as an increase in blood pressure, an increase in pulse rate, an increase in body temperature, or a change in an electric potential occurring during a heartbeat, which may be measured by an electrocardiogram. Among these changes, the increase in body temperature is the most representative sign of an abnormal state of a human body and is thus generally measured during a patient diagnosis in hospitals or general medical institutions. Conventionally, body temperature is measured using a mercury thermometer. Recently, various ear type thermometers for measuring a body temperature, i.e., inner body temperature without influence from external temperature, have been developed. In operation, such an ear type thermometer detects an amount of infrared rays emitted from an eardrum at an internal body temperature and converts the detected amount of infrared rays into a temperature value. The ear type thermometer is advantageous in that a measurement time is short and the body temperature can be conveniently measured by inserting the ear type thermometer into an ear.
A pulse indicates a dynamic extension of an artery that can be felt by a finger. Since the dynamic extension of an artery is due to a contraction of the heart, a heart rate, i.e., a heart's contraction rate, can be inferred from a pulse rate. When a human body is infected by a disease, the pulse rate, rhythm, or strength changes even when the human body is in a stable status. Accordingly, a person's state of health can be checked by measuring the pulse rate, rhythm, or strength.
Further, oxygen saturation indicates an amount of arterial blood (SpO2) in which oxygen is saturated. Oxygen saturation is measured to test a pulmonary function, estimate a concentration of oxygen in blood during oxygen therapy at home, or diagnose asthma and pulmonary emphysema. Human respiration is a process of discharging waste gas, i.e., carbonic acid gas, from a human body and providing oxygen to the human body. A human lung accommodates air coming from outside, emits carbonic acid gas, and absorbs oxygen. A pulmonary artery discharges carbonic acid gas collected throughout the human body through pulmonary alveoli using a difference in air pressure during exhalation. Conversely, blood in a pulmonary vein absorbs oxygen from inhaled air and then circulates to the heart. When respiration is unstable, a supply of oxygen is interrupted, which deteriorates the functions of a body's organs. In particular, oxygen saturation directly relates to an amount of oxygen supplied to the organs and thus provides very useful information regarding metabolism.
FIG. 1 shows an example of a conventional ear type thermometer for measuring body temperature. The ear type thermometer shown in FIG. 1 includes a housing 150 having a probe 110 through which infrared rays pass, a light receiver 120 that receives infrared rays emitted from at least one area from among a human eardrum and peripheral areas of the eardrum through the probe 110, a signal processor 130 that calculates a temperature from an output of the light receiver 120, and a display/sound unit 140 that displays the temperature.
The light receiver 120 includes a condenser device, which condenses infrared rays passing through the probe 110, and an infrared receiver device, which is disposed to receive the infrared rays condensed by the condenser device to receive infrared rays emitted from at least one area from among the eardrum and the peripheral areas of the eardrum.
Disadvantageously, the conventional ear type thermometer shown in FIG. 1 is a separate device that has to be additionally carried by a user. Moreover, a tip of the probe 110 of the thermometer needs to be in close contact with an internal surface of a subject's ear in order to accurately measure the subject's body temperature. However, when another person measures a subject's body temperature, the contact between the thermometer and the internal surface of the ear cannot be adjusted effectively. Although the subject can directly adjust the contact when measuring his own body temperature, the subject must remove the thermometer from the ear to view the display unit to check a measured value and verify whether the measurement has been accurately performed. Accordingly, this thermometer is not appropriate for self-diagnosis and is thus usually used when another person measures a subject's body temperature.
In order to apply such a conventional ear type thermometer to a remote medical treatment, since a measured value needs to be transmitted via a separate transmission apparatus, an interface is required. Accordingly, it is difficult to monitor results of the measurement frequently or for an extended period of time.
FIG. 2 shows an example of a conventional mobile apparatus that is capable of measuring a bio signal. The exemplary mobile apparatus shown in FIG. 2 is a portable communication terminal, which allows a function of a heart to be diagnosed or obesity to be tested based on a heart rate and a body fat rate, which are detected from a user's body. This apparatus eliminates an inconvenience of carrying a separate apparatus solely for measuring bio information. Electrodes 2a, 2b, 2c, and 2d are attached to an outer surface of a mobile communication terminal in order to measure a user's bio information.
FIG. 3 is a block diagram of the conventional mobile apparatus shown in FIG. 2. A portable communication terminal 300 includes a communication terminal module 320 and a bio-information measurement module 310 to provide dual functionality of voice communication and bio information measurement. The communication terminal module 320 includes a transceiver 326 as a user interface unit, a display unit 321, such as a liquid crystal display (LCD), allowing communication of character information, and an input unit 322 such as a keypad. The input unit 322 is used by a user to operate or control the portable communication terminal 300. Communication of information can be implemented by wireless transmission and reception of data via a wireless communication unit 323. A memory unit 324 stores information regarding the user of the portable communication terminal 300 and data necessary for the operation of the central controller 325.
The bio-information measurement module 310 includes a body fat measurer 311 and a heart rate measurer 312. An interface unit 313 performs data interface between the portable communication terminal 300 and an external electronic apparatus, for example, a removable bio-information measurement module.
FIG. 4 is a detailed block diagram of the heart rate measurer 312. The heart rate measurer 312 includes a voltage generator 401, electrodes 402, an amplifier 403, a pulse shaper 404, a pulse counter 405, and an interface unit 406. When the electrodes 402 of the voltage generator 401, which are attached to a main body of the portable communication terminal 300, are in close contact with a part of a subject's body, for example, right and left hands, a voltage change signal due to the heart's beat is detected. The voltage change signal is amplified by the amplifier 403, for example, a differential amplifier. The amplified voltage change signal is converted to a pulse signal by the pulse shaper 404. The pulse signal is counted by the pulse counter 405 to obtain a heart rate. An output signal of the pulse counter 405 is a digital signal and is input to the interface unit 406. The central controller (325 of FIG. 3) displays the heart rate on the display unit 321 and transmits it through the wireless communication unit 323. Voltage measurement electrodes used to measure body fat in the body fat measurer 311 are also used as the electrodes 402.
Disadvantageously, such a conventional portable communication terminal for measuring bio information using electrodes is influenced by a motion artifact caused by a force pressing the electrodes and is sensitive to contamination of the electrodes or the skin since the electrodes directly contact the skin. When the electrodes are exposed outside the communication terminal, they are easily damaged or contaminated.
To obtain bio information, such as oxygen saturation, a component in blood needs to be detected. Accordingly, a method of applying signals showing different characteristics according to concentrations of oxidized hemoglobin and reduced hemoglobin and obtaining the bio information using a difference between the signals is usually used. In conventional methods, however, since one electrode cannot apply different types of signals, bio information beyond a pulse rate cannot be appropriately measured.